Imaging lens

ABSTRACT

An imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens having positive refractive power; a fourth lens having negative refractive power; and a fifth lens having object-side and image plane-side surfaces thereof being aspheric, arranged in this order from an object side to an image plane side. The first lens has a shape so that a curvature radius of a surface thereof on the object side is positive. The fifth lens has a shape so that a curvature radius of the surface thereof on the object side and a curvature radius of the surface thereof on the image plane side are positive. The second lens, the third lens, and the fourth lens are arranged so that a specific conditional expression is satisfied.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of a prior application Ser. No.13/494,406, filed on Jun. 12, 2012, pending, which claims priority ofJapanese Patent Application No. 2011-143711, filed on Jun. 29, 2011.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an imaging lens for forming an image onan imaging element such as a CCD sensor and a CMOS sensor. Morespecifically, the present invention relates to an imaging lens that issuitable for mounting on a relatively small camera such as a cellularphone, a digital still camera, a portable information terminal, asecurity camera, a vehicle onboard camera, and a network camera.

An imaging Lens for mounting on a small camera is required not only tobe composed of a small number of lenses, but also to have aconfiguration that can attain high resolution, so as to be compatiblewith a high-resolution imaging element that has been available in recentyears. Conventionally, a three-lens imaging lens configuration has beenoften used as such an imaging lens. As the resolution of the imagingelement has been increased, it is more difficult to achieve satisfactoryperformance only with the three-lens configuration. In these years, afour-lens configuration or five-lens configuration has being used morefrequently.

Among these lens configurations, because of higher design flexibility,the five-lens configuration is expected to be a lens configuration to beused in the next generation imaging lens. As an imaging lens having suchthe five-lens configuration, for example, an imaging lens described inPatent Reference has been known.

According to Patent Reference, the imaging lens includes in the orderfrom an object side: a first lens that has a convex object side surfaceand is positive; a second lens that has a shape of a negative meniscuslens directing a concave surface thereof to an image plane side; a thirdlens that has a shape of positive meniscus lens directing a convexsurface thereof to the image plane side; a negative fourth lens that hasan aspheric shape on the both sides and has a concave image plane sidesurface near an optical axis; and a fifth lens that has an asphericshape on the both sides and is positive or negative.

In the lens configuration, a lower limit of Abbe's number of the firstlens, and upper limits of Abbe's numbers of the second and the fourthlenses are set respectively, so as to correct an axial chromaticaberration and a chromatic aberration of magnification and thereby becompatible with high performances of the imaging lens.

Patent Reference: Japanese Patent Publication No. 2007-264180

According to the imaging lens described in Patent Reference, it ispossible to attain relatively satisfactory aberrations. Since the totallength of the lens system is long, however, it is difficult to attainboth miniaturization of the imaging lens and satisfactory aberrationcorrection.

In view of the problems of the conventional techniques described above,an object of the present invention is to provide an imaging lens thatcan satisfactorily correct aberrations in spite of a small size thereof.

SUMMARY OF THE INVENTION

In order to attain the object described above, according to the presentinvention, an imaging lens includes a first lens having positiverefractive power; a second lens having negative refractive power; athird lens having positive refractive power; a fourth lens havingnegative refractive power; and a fifth lens having negative refractivepower, arranged un this order from an object side to an image planeside. The first lens is formed in a shape so that a curvature radius onan object side surface thereof is positive, the second lens is formed ina shape so that a curvature radius of an object side surface thereof anda curvature radius of an image side surface thereof are both positive,the third lens is formed in a shape so that a curvature radius of anobject side surface thereof is positive, and the fifth lens is formed ina shape so that a curvature radius of an object side surface thereof anda curvature radius of an image side surface thereof are both positive.

In the configuration, when the first lens has a focal length f1, thesecond lens has a focal length f2, the third lens has a focal length f3,the fourth lens has a focal length f4, and the fifth lens has a focallength f5, the imaging lens satisfies the following conditionalexpressions (1) and (2):

f1<f3 and |f2|<f3   (1)

f3<|f4| and |f2<|f5|  (2)

When the imaging lens satisfies the conditional expressions (1) and (2),it is possible to satisfactorily correct aberrations while attainingminiaturization of the imaging lens. In case of the imaging lens havingthe above-described configuration, since the first lens and the secondlens have strong refractive power in relative to those of the otherthree lenses, the refractive power of the whole lens system in focusedon the object side.

Therefore, it is possible to somewhat compress the total optical lengthwhile securing a certain imaging angle of view. In addition, accordingto the invention, the respective lenses of the third lens to the fifthlens have relatively weak refractive, powers. Aberrations generated inthe first lens and the second lens, which have strong refractive powers,are suitably corrected through those third to fifth lenses, which haveweak refractive powers.

Here, the relation between the focal length of the second lens and thefocal length of the third lens, and the relation between the focallength of the second lens and the focal length of the fifth lenspreferably satisfy the following conditional expressions:

3×|f2|<f3 and 3×|f2|<|f5|  (3)

In the imaging lens having the above-described configuration, it ispreferred to form the fourth lens in a shape so that a curvature radiusof an object side surface thereof and a curvature radius of the imageside surface thereof are both negative.

As described above, the second lens is formed in a shape so that thecurvature radius of the object side surface thereof and the curvatureradius of the image side surface thereof are both positive, i.e. a shapeof a meniscus lens directing a convex surface thereof to the objectside. When the fourth lens is formed in a shape so that a curvatureradius of an object side surface thereof and a curvature radius of animage side surface thereof are both negative, i.e., a shape of ameniscus lens directing a concave surface thereof to the object side,the second and the fourth lens are arranged both directing their concavesurfaces to the third lens. For this reason, aberrations generated inthe first lens are suitably corrected also by thenegative-positive-negative arrangement of refractive powers of thesecond lens to the fourth lens, and the shapes of the respective lenssurfaces of second and fourth lenses.

When the first lens has Abbe's number νd1, the second lens has Abbe'snumber νd2, the third lens has Abbe's number νd3, the fourth lens hasAbbe's number νd4, and the fifth lens has Abbe's number νd5, the imaginglens having the above-described configuration preferably satisfies thefollowing conditional expressions (4) to (8):

45<νd1<85   (4)

νd1<35   (5)

45<νd3<85   (6)

νd4<35   (7)

45<νd5<85   (8)

When the imaging lens satisfies the conditional expressions (4) to (8),it is possible to satisfactorily correct axial chromatic aberration andan off-axis chromatic aberration of magnification. According to theconditional expressions (4) to (8), the second lens and the fourth lensare made of a high-dispersion material, and the first lens, third lens,and the fifth lens are made of a low-dispersion material. Accordingly,in the imaging lens of the invention, since a high-dispersion materialand a low-dispersion material are alternately disposed, the axialchromatic aberration and the off-axis chromatic aberration ofmagnification are suitably corrected.

When the whole lens system has a focal length f and the second lens hasthe focal length f2, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(9):

−1.5<f2/f<−0.4   (9)

When the imaging lens satisfies the conditional expression (9), it ispossible to restrain the chromatic aberrations and a field curvaturewithin preferred ranges. When the value exceeds the upper limit “−0.4”,the second lens has strong refractive power in relative to that of thewhole lens system, so that the axial and the off-axis chromaticaberrations are excessively corrected (that of a short wavelengthincreases in the positive direction in relative to that of a referencewavelength). In addition, the image-forming surface curves to the imageplane side, and it is difficult to obtain satisfactory image-formingperformance.

On the other hand, when the value is below the lower limit “−1.5”, thesecond lens has weak refractive power in relative to that of the wholelens system, so that the axial and off-axis chromatic aberrations areinsufficiently corrected (that of a short wavelength increases in thenegative direction in relative to that of a reference wavelength).Moreover, the image-forming surface curves to the object side, and it isdifficult to obtain satisfactory image-forming performance also in thiscase.

When the first lens has the focal length f1 and the second lens has thefocal length f2, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(10):

−1.0<f1/f2<−0.5   (10)

When the imaging lens satisfies the conditional expression (10), it ispossible to restrain an astigmatism, a field curvature, and a chromaticaberration within preferred ranges in a balanced manner, whilerestraining a Petzval sum of the whole lens system near zero. When thevalue exceeds the upper limit “−0.5”, the first lens has strongrefractive power In relative to that of the second lens, so that theaxial and the off-axis chromatic aberrations are insufficientlycorrected. As for the astigmatism, a tangential image surface tilts inthe negative direction and the astigmatic difference increases. For thisreason, it is difficult to obtain satisfactory image-formingperformance.

On the other hand, when the value is below the lower limit “−1.0”, thefirst lens has weak refractive power in relative to that of the secondlens, so that negative refractive power is strong and the axial and theoff-axis chromatic aberrations are excessively corrected. In addition,the image-forming surface curves towards the image plane side. As forthe astigmatism, the tangential image surface tilts in the positivedirection and the astigmatic difference increases. Therefore also inthis case, it is difficult to obtain satisfactory image-formingperformance.

When a curvature radius of an object side surface of the second lens isR2f and a curvature radius of an image side surface thereof is R2r, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (11):

3.0<R2f/R2r<6.0   (11)

When the imaging lens satisfies the conditional expression (11), it ispossible to restrain a coma aberration, field curvature, and chromaticaberrations within preferred ranges, respectively. When the valueexceeds the upper limit “6.0”, the second lens has relatively strongrefractive power, an outer coma aberration of an off-axis light beamincreases, and the axial and the off-axis chromatic aberrations areexcessively corrected. In addition, since the image-forming surfacecurves to the image plane side, it is difficult to obtain satisfactoryimage-forming performance.

On the other hand, when the value is below the lower limit “3.0”, thesecond lens has relatively weak refractive power, and the axial and theoff-axis chromatic aberrations are insufficiently corrected. Inaddition, since the image-forming surface curves to the object side, itis difficult to obtain satisfactory image-forming performance also inthis case.

When the whole lens system has the focal length f and the third lens hasthe focal length f3, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(12):

3.0<f3/f<7.0   (12)

As described above, according to the imaging lens of the invention, thethird lens mainly works for correcting aberrations. When the imaginglens satisfies the conditional expression (12), it is possible tosatisfactorily correct aberrations while attaining miniaturization ofthe imaging lens. When the value exceeds the upper limit “7.0”, thethird lens has weak refractive power in comparison with that of thewhole lens system, and it is difficult to attain miniaturization of theimaging lens.

Here, when the third lens has weak refractive power, it is possible toattain miniaturization of the imaging lens by increasing the refractivepower of the fourth lens or the fifth lens. In this case, however, it isdifficult to correct aberrations (especially correction of the comaaberration), it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limit“3.0”, although such low value is advantageous for miniaturization ofthe imaging lens, the coma aberration increases and the astigmaticdifference also increases. Therefore, also in this case, it is difficultto obtain satisfactory image-forming performance.

When the maximum effective diameter of the object side surface of thethird lens is φ_(3A), the maximum effective diameter of the image sidesurface thereof is φ_(3B), maximum effective diameter of the object sidesurface of the fourth lens is φ_(4A), maximum effective diameter of theimage side surface thereof is φ_(4B), and an absolute value of themaximum sag in the range that is up to the 70% value of the maximumeffective diameters φ_(3A) to φ_(4B) of those surfaces is Z_(0.7), theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (13):

Z _(0.7) /f<0.1   (13)

As described above, when the maximum sag is restrained within a certainrange, the third lens and the fourth lens have substantially uniformthicknesses in an optical axis direction and have less curved shapes.According to such third lens and fourth lens, it is possible to restraingeneration of aberrations of complicated shapes and to satisfactorilycorrect aberrations generated in the first lens and the second lens. Inaddition, it is also possible to decrease sensitivity to deteriorationof image-forming performance due to de-centering (imperfect alignment),tilting, and the like, which occur upon production of the imaging lens,i.e., sensitivity to production errors.

Moreover, since the thicknesses in the optical axis direction aresubstantially uniform, it is possible to improve fabrication performanceupon production and restrain the manufacturing cost of the imaging lens.Here, “sag” means a distance from a tangential plane of each surface,which is orthogonal to the optical axis, to the surface in a directionparallel to the optical axis.

When the whole lens system has the focal length f and a composite focallength of the third lens and the fourth lens is f34, the imaging lenshaving the above-described configuration preferably satisfies thefollowing conditional expression (14):

2.0<f34/f<10.0   (14)

When a ratio of the composite focal length of the third lens and thefourth lens to the focal length of the whole lens system is restrainedwithin the range defined by the conditional expression (14), it ispossible to more satisfactorily correct aberrations. When the valueexceeds the upper limit “10.0”, the composite refractive power of thethird lens and the fourth lens is relatively weak and it is difficult torestrain aberrations within preferred ranges in a balanced manner. Onthe other hand, when the value is below the lower limit “2.0”, thecomposite refractive power of the third lens and the fourth lens isrelatively strong, so that it is advantageous for correcting adistortion, but the astigmatic difference increases and it is difficultto obtain satisfactory image-forming performance.

When a distance on the optical axis from the image side surface of thesecond lens to the object side surface of the third lens is dA and adistance on the optical axis from the image side surface of the thirdlens to the object side surface of the fourth lens is dB, the imaginglens having the above-described configuration preferably satisfies thefollowing conditional expression (15):

0.3<dA/dB<2.0   (15)

As well known in the art, there is a limit in an incident angle of alight beam that an imaging element such as a CCD sensor and a CMOSsensor can take, in view of an imaging element structure. When an exitangle of an off-axis light beam is outside the range, light beamsoutside the range are not taken by the sensor, which results in aso-called “shading phenomenon”. More specifically, an image takenthrough the imaging lens may have a dark portion on periphery thereof inrelative to a center portion.

When the imaging lens satisfies the conditional expression (15), it ispossible to keep the maximum exit angle of the off-axis light beam smallwhile attaining miniaturization of the imaging lens. When the valueexceeds the upper limit “2.0”, although it is easy to keep the maximumexit angle of the off-axis light beam small, it is difficult to attainminiaturization of the imaging lens. On the other hand, when the valueis below the lower limit “0.3”, although it is advantageous forminiaturization of the imaging lens, a chromatic aberration isinsufficiently corrected and it is difficult to obtain satisfactoryimaging performance. In addition, the maximum exit angle of the off-axislight beam increases and thereby the shading phenomenon easily occurs.

According to the imaging lens of the invention, it is possible to attainboth miniaturization of the imaging lens and satisfactory aberrationcorrection, and to provide a small imaging lens with satisfactorilycorrected aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing a configuration of animaging lens in Numerical Data Example 1 according to an embodiment ofthe invention;

FIG. 2 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 1;

FIG. 3 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 1;

FIG. 4 is a schematic sectional view showing a configuration of animaging lens in Numerical Data Example 2 according to an embodiment ofthe invention;

FIG. 5 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 4;

FIG. 6 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 4;

FIG. 7 is a schematic sectional view showing a configuration of animaging lens in Numerical Data Example 3 according to an embodiment ofthe invention;

FIG. 8 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 7;

FIG. 9 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 7;

FIG. 10 is a schematic sectional view showing a configuration of animaging lens in Numerical Data Example 4 according to an embodiment ofthe invention;

FIG. 11 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 10;

FIG. 12 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 10;

FIG. 13 is a schematic sectional view showing a configuration of animaging lens in Numerical Data Example 5 according to an embodiment ofthe invention;

FIG. 14 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 13;

FIG. 15 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 13

FIG. 16 is a schematic sectional view showing a configuration of animaging lens in Numerical Data Example 6 according to an embodiment ofthe invention;

FIG. 17 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 16; and

FIG. 18 is an aberration diagram showing a spherical aberration, anastigmatism, and a distortion of the imaging lens of FIG. 16.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, referring to the accompanying drawings, preferred embodimentsof the present invention will be fully described.

FIGS. 1, 4, 7, 10, 13, and 16 are sectional views of imaging lenses inNumerical Data Examples 1 to 6 according to the embodiment,respectively. Since a basic lens configuration is the same among theNumerical Data Examples, the lens configuration of the embodiment willbe described with reference to the sectional view of Numerical DataExample 1.

As shown in FIG. 1, the imaging lens of this embodiment includes a firstlens L1 having positive refractive power; a second lens L2 havingnegative refractive power; a third lens L3 having positive refractivepower; a fourth lens L4 having negative refractive power; and a fifthlens L5 having negative refractive power, arranged in this order from anobject side to an image plane side. A filter 10 such as an infraredcut-off filter and a cover glass is provided between the fifth lens L5and the image plane IM. The filter 10 may be also optionally omitted.Here, in the imaging lens of this embodiment, there is an aperture stopprovided on an object side surface of the first lens L1.

Each lens of the first lens L1 to the fifth lens L5 satisfies thefollowing conditional expressions (1) and (2):

f1<f3 and |f2|<f3   (1)

f3<|f4| and |f2|<|f5|  (2)

In the above-conditional expressions,

f1: Focal length of the first lens L1f2: Focal length of the second lens L2f3: Focal length of the third lens L3f4: Focal length of the fourth lens L4f5: Focal length of the fifth lens L5

As described above, in the imaging lens of this embodiment, therefractive powers of the first lens L1 and the second lens L2 arestronger than those of the other three lenses, and the refractive powerof the whole lens system is focused on the object side. With thisconfiguration, it is possible to attain miniaturization of the imaginglens and suitably correct aberrations generated in the first lens L1 andthe second lens L2 through the respective lenses from the third lens L3to the fifth lens L5, which have weak refractive powers. Here, theimaging lens of this embodiment satisfies the following conditionalexpression (3) in addition to the above-described conditionalexpressions (1) and (2):

3×|f2|<f3 and 3×|f2|<f5|  (3)

Furthermore, the imaging lens of this embodiment satisfies the followingconditional expressions (4) to (8):

45<νd1<85   (4)

νd2<35   (5)

45<νd3<85   (6)

νd4<35   (7)

45<νd5<85   (8)

In the above-conditional expressions,νd1: Abbe's number of the first lens L1νd2: Abbe's number of the second lens L2νd3: Abbe's number of the third lens L3νd4: Abbe's number or the fourth lens L4νd5: Abbe's number of the fifth lens L5

As shown in the conditional expressions (4) to (8), in the imaging lensof the embodiment, a high-dispersion material and a low-dispersionmaterial are alternately used in combination. When the Abbe's number ofeach lens is restrained within the range defined by the conditionalexpressions (4) to (8), it is possible to satisfactorily correct anaxial chromatic aberration and an off-axis chromatic aberration ofmagnification.

According to the imaging lens having the above-described configuration,the first lens L1 is formed in a shape so that a curvature radius R1 ofan object side surface thereof is positive and a curvature radius R2 ofan image side surface thereof is negative, i.e. a shape of a biconvexlens near an optical axis X. Here, the shape of the first lens L1 is notlimited to such shape of a biconvex lens near the optical axis X. Thefirst lens L1 can have any shape as long as the curvature radius R1 ofthe object side surface thereof is positive, and can be formed in ashape so that the curvature radii R1 and R2 are both positive, i.e. ashape of a meniscus lens directing a convex surface thereof to theobject side near the optical axis X.

The second lens L2 is formed in a shape so that a curvature radius R3 ofan object side surface thereof and a curvature radius R4 of an imageside surface thereof are both positive so as to have a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. In addition, the second lens L2 is formed so as tosatisfy the following conditional expressions (9) and (11). The secondlens L2 and the first lens L1 are lenses having strong refractive powersamong the lenses in the lens system. According to this embodiment, thefirst lens L1 and the second lens L2 satisfy the following conditionalexpression (10). When the imaging lens of the embodiment satisfies theconditional expression (10), it is possible to restrain the Petzval sumof the whole lens system near zero and restrain an astigmatism, fieldcurvature, and chromatic aberration within preferred ranges in abalanced manner.

−1.5<f2/f<−0.4   (9)

−1.0<f1/f2<−0.5   (10)

3.0<R2f/R2r<6.0   (11)

In the above-conditional expressions,

R2f: Curvature radius of an object side surface of the second lens L2R2r: Curvature radius of an image side surface of the second lens L2

In order to more satisfactorily correct aberrations, the imaging lenspreferably further satisfies the following conditional expression (10A).The imaging lenses of Numerical Data Examples 1, 5, and 6 satisfy thefollowing conditional expression (10A):

−0.7<f1/f2<−0.5   (10A)

The third lens L3 is formed in a shape so that a curvature radius R5 ofan object side surface and a curvature radius R6 of an image sidesurface are both positive, so as to have a shape of a meniscus lensdirecting a convex surface to the object side near the optical axis X.The shape of the third lens L3 is not limited to the shape of a meniscuslens directing a convex surface thereof to the object side near theoptical axis X. The third lens L3 can have any shape as long as thecurvature radius R5 of the object side surface is positive and can havea shape of a biconvex lens near the optical axis X. Numerical DataExamples 1 to 5 show examples, in which the third lens L3 has a shape ofa meniscus lens directing a convex surface thereof to the object sidenear the optical axis X, and Numerical Data Example 6 shows an example,in which the third lens L3 has a shape of a biconvex lens near theoptical axis X.

The third lens L3 satisfies the following conditional expression (12).With this configuration, it is possible to more satisfactorily correctaberrations. In order to more satisfactorily correct aberrations, it ispreferred to further satisfy the following conditional expression (12A).The imaging lenses according to Numerical Data Example 1 and NumericalData Example 3 to 6 satisfy the conditional expression (12A):

3.0<f3/f<7.0   (12)

4.0<f3/f<7.0   (12A)

The fourth lens L4 is formed in a shape so that a curvature radius R7 ofan object side surface and a curvature radius R8 of an image sidesurface are both negative, i.e. a shape of a meniscus lens directing aconcave surface to the object side near the optical axis X. As describedabove, since the second lens L2 is formed in a shape of a meniscus lensdirecting a convex surface to the object side near the optical axis X,when the fourth lens L4 is formed in a shape of a meniscus lensdirecting a concave surface to the object side near the optical axis X,the second lens L2 and the fourth lens L4 are arranged both directingtheir concave surfaces to the third lens L3. For this reason,aberrations generated in the first lens L1 are suitably corrected by thenegative-positive-negative arrangement of refractive powers of thesecond lens L2 to the fourth lens L4 and the shapes of the respectivelens surfaces of the second lens L2 and the fourth lens L4.

The third lens L3 and the fourth lens L4 mainly work for correctingaberrations. The imaging lens of the embodiment satisfactorily correctsaberrations by restraining the sag of each lens surface of the thirdlens L3 and the fourth lens L4 within a certain range. Morespecifically, when the maximum effective diameter of the object sidesurface of the third lens L3 is φ_(3A), the maximum effective diameterof the image side surface thereof is φ_(3B), the maximum effectivediameter of the object side surface of the fourth lens L4 is φ_(4A), themaximum effective diameter of the image side surface thereof is φ_(4B),and the absolute value of the maximum sag in the range that is up to 70%value of the maximum effective diameters φ_(3A) to φ_(4B) is Z_(0.7),the imaging lens preferably satisfies the following conditionalexpression (13):

Z _(0.7) /f<0.1   (13)

Restraining the maximum sag within the range defined by the conditionalexpression (13), the third lens L3 and the fourth lens L4 havesubstantially uniform thicknesses in a direction of the optical axis Xand have less curved shapes. With such lens shapes, it is possible tomore satisfactorily correct aberrations. In addition, it is alsopossible to effectively decrease the sensitivity to deterioration ofimage-forming performance due to de-centering (imperfect alignment),tilting, or the like, which is generated upon production of the imaginglens, i.e. so-called “production error sensitivity”. Moreover, withsubstantially uniform thicknesses in the direction of the optical axisX, it is possible to improve the fabrication performance upon productionand thereby restrain the manufacturing cost of the imaging lens. Here,the sag refers to a distance from a tangential plane of each surface,which is orthogonal to the optical axle X, to the surface in a directionparallel to the optical axis X.

Here, each lens from the second lens L2 to the fourth lens L4 satisfiesthe following conditional expressions (14) and (15). With thisconfiguration, it is possible to more satisfactorily correctaberrations. In addition, the maximum exit angle of the off-axis lightbeam is kept small and generation of the shading phenomenon isrestrained.

2.0<f34/f<10.0   (14)

0.3<dA/dB<2.0   (15)

In the above-conditional expressions,f34: Composite focal length of the third lens L3 and the fourth lens L4dA: Distance on the optical axis from the image side surface of thesecond lens L2 to the object side surface of the third lens L3dB: Distance on the optical axis from the image side surface of thethird lens L3 to the object side surface of the fourth lens L4

In order to more satisfactorily correct aberrations, the imaging lenssatisfies the following conditional expressions (14A) and (15A). Theimaging lenses according to Numerical Data Example 1 and Numerical DataExamples 3 to 6 satisfy the conditional expression (14A). The imaginglens according to Numerical Data Example 1 to 6 satisfies theconditional expression (15A).

4.0<f34/f<10.0   (14A)

0.3<dA/dB<1.5   (15A)

The fifth lens L5 is formed in a shape so that a curvature radius R9 ofan object side surface and a curvature radius R10 of an image sidesurface are both positive so as to have a shape of a meniscus lensdirecting a convex surface thereof to the object side near the opticalaxis X. In addition, the image side surface of the fifth lens L5 isformed as an aspheric shape so as to have a convex shape on the objectside near the optical axis X and has a concave shape on the object sidein the periphery. With such shape of the fifth lens L5, it is possibleto suitably restrain an incident angle of a light beam emitted from theimaging lens to the image plane.

Here, it is not necessary to satisfy all of the conditional expressions(1) to (15). When any single one of the conditional expressions (1) to(15) is individually satisfied, it is possible to obtain an effectcorresponding to the respective conditional expression.

In the embodiment, each lens has a lens surface that is formed as anaspheric surface. When the aspheric surfaces applied to the lenssurfaces have an axis Z in the optical axis direction, a height H in adirection perpendicular to the optical axis, a conical coefficient k,and aspheric coefficients A₄, A₆, A₈, A₁₀, A₁₂, A₁₄, and A₁₆, a shape ofthe aspheric surfaces of the lens surfaces may be expressed as follows:

$\begin{matrix}{Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Next, Numerical Data Examples of the embodiment will be described. Ineach of the Numerical Data Examples, f represents a focal length of awhole lens system, Fno represents an F number, and ω represents a halfangle of view, respectively. In addition, i represents a surface numbercounted from the object side, R represents a curvature radius, drepresents a distance between lens surfaces (surface spacing) on theoptical axis, Nd represents a refractive index for a d line, and νdrepresents Abbe's number for the d line, respectively. Here, asphericsurfaces are indicated with surface numbers i affixed with * (asterisk).Furthermore, L represents a distance on the optical axis from the objectside surface of the first lens L1 to the image plane IM.

NUMERICAL DATA EXAMPLE 1

Basic lens data are shown below.

f = 3.981 mm, Fno = 2.31, ω = 32.16° Unit: mm Surface Data SurfaceNumber i R d Nd νd (Object) ∞ ∞  1* (Stop) 1.637 0.600 1.5346 56.0(=νd1)  2* −32.616 0.050  3* 6.151 (=R2f) 0.320 1.6142 26.0 (=νd2)  4*1.956 (=R2r) 0.393 (=dA)  5* 11.050 0.436 1.5346 56.0 (=νd3)  6* 577.4510.368 (=dB)  7* −15.454 0.400 1.6142 26.0 (=νd4)  8* −18.961 0.157  9*1.508 0.696 1.5346 56.0 (=νd5) 10* 1.256 0.235 11 ∞ 0.300 1.5163 64.1212 ∞ 0.767 (Image Plane) ∞ f1 = 2.934 mm f2 = −4.809 mm f3 = 21.068 mmf4 = −142.204 mm f5 = −338.358 mm f34 = 24.831 mm Z_(0.7) = 0.054 mm L =4.62 mm Aspheric Surface Data First Surface k = 0.000,  A₄ = −2.872E−03, A₆ = −1.595E−03,  A₈ = 2.064E−02, A₁₀ = −2.880E−02 Second Surface k =0.000,  A₄ = −7.666E −02,  A₆ = 2.609E−01,  A₈ = −3.765E−01, A₁₀ =1.617E−01 Third Surface k = 0.000,  A₄ = −1.611E−01,  A₆ = 4.112E−01, A₈ = −6.070E−01, A₁₀ = 3.079E−01 Fourth Surface k = 0.000,  A₄ =−9.785E−02,  A₆ = 2.488E−01,  A₈ = −3.216E−01, A₁₀ = 1.681E−01 FifthSurface k = 0.000,  A₄ = −1.150E−01,  A₆ = 1.621E−01,  A₈ = −9.680E−02,A₁₀ = 2.778E−02 Sixth Surface k = 0.000,  A₄ = −1.711E−01,  A₆ =2.129E−01,  A₈ = −2.767E−01, A₁₀ = 2.476E−01 A₁₂ = −1.092E−01, A₁₄ =1.524E−02, A₁₆ = 3.922E−03 Seventh Surface k = 0.000,  A₄ = 1.025 −01, A₆ = −1.608E−01,  A₈ = 8.611E−02, A₁₀ = −2.751E−02 A₁₂ = −4.373E−03,A₁₄ = 1.437E−03, A₁₆ = 2.803E−05 Eighth Surface k = 0.000,  A₄ =−3.790E−02,  A₆ = 6.322E−02,  A₈ = −4.773E−02, A₁₀ = 1.355E−02, A₁₂ =−3.741E−03, A₁₄ = 1.293E−03, A₁₆ = −1.694E−04 Ninth Surface k = −3.022 A₄ = −3.313E−01,  A₆ = 1.694E−01,  A₈ = −4.558E−02, A₁₀ = 1.782E−03 A₁₂= 9.158E−04, A₁₄ = 1.850E−04, A₁₆ = −5.656E−05 Tenth Surface k = −3.401 A₄ = −1.661E−01,  A₆ = 7.946E−02,  A₈ = −3.006E−02, A₁₀ = 7.850E−03,A₁₂ = −1.649E−03, A₁₄ = 2.468E−04, A₁₆ = −1.788E−05The values of the respective conditional expressions are as follows:f2/f=−1.208f1/f2=−0.610R2f/R2r=3.145f3/f=5.292Z_(0.7)/f=0.013f34/f=6.237dA/dB=1.068

Accordingly, the imaging lens of this Numerical Data Example 1 satisfiesthe respective conditional expressions (1) to (15).

FIG. 2 shows the lateral aberration that corresponds to a ratio H of animage height to the maximum image height (hereinafter referred to as“image height ratio H”) in the imaging lens of Numerical Data Example 1by dividing into a tangential direction and a sagittal direction (whichis also the same in FIGS. 5, 8, 11, 14, and 17). Furthermore, FIG. 3shows a spherical aberration (mm), an astigmatism (mm), and a distortion(%) of the imaging lens of Numerical Data Example 1, respectively. Inthe aberration diagrams, lateral aberration diagrams and sphericalaberration diagrams show aberrations for a g line (435.84 nm), an F line(486.13 nm), an e line (546.07 nm), a d line (587.56 nm), and a C line(656.27 nm), and astigmatism diagram shows the aberration on thesagittal image surface S and the aberration on the tangential imagesurface T, respectively (which are the same in FIGS. 6, 9, 12, 15, and18). As shown in FIGS. 2 and 3, according to this Numerical Data Example1, it is possible, to satisfactorily correct aberrations.

NUMERICAL DATA EXAMPLE 2

Basic lens data are shown below.

f = 3.976 mm, Fno = 2.42, ω = 32.16° Unit: mm Surface Data SurfaceNumber i R d Nd νd (Object) ∞ ∞  1* (Stop) 1.558 0.600 1.5346 56.0(=νd1)  2* −12.051 0.068  3* 9.638 (=R2f) 0.320 1.6142 26.0 (=νd2)  4*1.629 (=R2r) 0.250 (=dA)  5* 3.657 0.597 1.5346 56.0 (=νd3)  6* 7.7590.430 (=dB)  7* −17.253 0.363 1.6142 26.0 (=νd4)  8* −18.743 0.123  9*1.475 0.707 1.5346 56.0 (=νd5) 10* 1.218 0.235 11 ∞ 0.300 1.5163 64.1212 ∞ 0.689 (Image Plane) ∞ f1 = 2.621 mm f2 = −3.242 mm f3 = 12.317 mmf4 = −389.265 mm f5 = −348.964 mm f34 = 12.778 mm Z_(0.7) = 0.055 mm L =4.58 mm Aspheric Surface Data First Surface k = 0.000,  A₄ = 7.436E−04, A₆ = −1.697E−03,  A₈ = 3.632E−02, A₁₀ = −4.223E−02 Second Surface k =0.000,  A₄ = 5.202E −02,  A₆ = 1.418E−01,  A₈ = −3.879E−01, A₁₀ =2.062E−01 Third Surface k = 0.000,  A₄ = −3.663E−02,  A₆ = 2.840E−01, A₈ = −6.571E−01, A₁₀ = 3.960E−01 Fourth Surface k = 0.000,  A₄ =−1.159E−01,  A₆ = 3.142E−01,  A₈ = −4.591E−01, A₁₀ = 2.641E−01 FifthSurface k = 0.000,  A₄ = −1.049E−01,  A₆ = 1.795E−01,  A₈ = −1.117E−01,A₁₀ = 2.213E−02 Sixth Surface k = 0.000,  A₄ = −1.107E−01,  A₆ =1.462E−01,  A₈ = −2.267E−01, A₁₀ = 2.435E−01 A₁₂ = −1.238E−01, A₁₄ =2.546E−02, A₁₆ = −1.262E−03 Seventh Surface k = 0.000,  A₄ = 1.915E−01, A₆ = −2.620E−01,  A₈ = 1.558E−01, A₁₀ = −5.362E−02 A₁₂ = −1.039E−02,A₁₄ = 1.172E−02, A₁₆ = −1.809E−03 Eighth Surface k = 0.000,  A₄ =6.708E−03,  A₆ = 3.015E−02,  A₈ = −4.305E−02, A₁₀ = 1.452E−02, A₁₂ =−3.583E−03, A₁₄ = 1.332E−03, A₁₆ = −2.117E−04 Ninth Surface k = −4.937 A₄ = −3.147E−01,  A₆ = 1.677E−01,  A₈ = −4.332E−02, A₁₀ = 1.805E−03 A₁₂= 8.019E−04, A₁₄ = 1.304E−04, A₁₆ = −4.485E−05 Tenth Surface k = −4.122, A₄ = −1.684E−01,  A₆ = 8.590E−02,  A₈ = −3.445E−02, A₁₀ = 9.084E−03,A₁₂ = −1.696E−03, A₁₄ = 2.153E−04, A₁₆ = −1.435E−05

The values of the respective conditional expressions are as follows:

f2/f=−0.815f1/f2=−0.808R2f/R2r=5.917f3/f=3.098Z_(0.7)/f=0.014f34/f=3.214dA/dB=0.581

Accordingly, the imaging lens of this Numerical Data Example 2 satisfiesthe respective conditional expressions (1) to (15).

FIG. 5 shows the lateral aberration that corresponds to the image heightratio H in the imaging lens of Numerical Data Example 2. Furthermore,FIG. 6 shows a spherical aberration (mm), an astigmatism (mm), and adistortion (%), respectively. As shown in FIGS. 5 and 6, also with theimaging lens of this Numerical Data Example 2, the image surface issatisfactorily corrected and aberrations are suitably corrected,similarly to Numerical Data Example 1.

NUMERICAL DATA EXAMPLE 3

Basic lens data are shown below.

f = 5.905 mm, Fno = 3.61, ω = 25.37° Unit: mm Surface Data SurfaceNumber i R d Nd νd (Object) ∞ ∞  1* (Stop) 1.715 0.820 1.5346 56.0(=νd1)  2* −9.433 0.058  3* 8.995 (=R2f) 0.448 1.6142 26.0 (=νd2)  4*1.512 (=R2r) 0.345 (=dA)  5* 4.101 0.770 1.5346 56.0 (=νd3)  6* 5.0600.557 (=dB)  7* −5.909 0.453 1.6142 26.0 (=νd4)  8* −6.261 0.71  9*2.133 0.696 1.5346 56.0 (=νd5) 10* 1.822 0.235 11 ∞ 0.300 1.5163 64.1212 ∞ 1.248 (Image Plane) ∞ f1 = 2.786 mm f2 = −3.028 mm f3 = 31.642 mmf4 = −336.142 mm f5 = −105.912 mm f34 = 35.707 mm Z_(0.7) = 0.121 mm L =6.00 mm Aspheric Surface Data First Surface k = 0.000,  A₄ = 2.748E−03, A₆ = −6.028E−03,  A₈ = 3.410E−02, A₁₀ = −2.208E−02 Second Surface k =0.000,  A₄ = 9.597E−02,  A₆ = 1.868E−01,  A₈ = −4.090E−01, A₁₀ =2.008E−01 Third Surface k = 0.000,  A₄ = 1.786E−02,  A₆ = 3.030E−01,  A₈= −5.887E−01, A₁₀ = 2.732E−01 Fourth Surface k = 0.000,  A₄ =−1.254E−01,  A₆ = 3.624E−01,  A₈ = −4.699E−01, A₁₀ = 2.040E−01 FifthSurface k = 0.000,  A₄ = −1.074E−01,  A₆ = 1.674E−01,  A₈ = −8.020E−02,A₁₀ = 1.429E−02 Sixth Surface k = 0.000,  A₄ = −9.229E−02,  A₆ =1.300E−01,  A₈ = −2.237E−01, A₁₀ = 2.431E−01, A₁₂ = −1.248E−01, A₁₄ =2.626E−02, A₁₆ = −2.083E−04 Seventh Surface k = 0.000,  A₄ = 1.722E−01, A₆ = −2.438E−01,  A₈ = 1.486E−01, A₁₀ = −5.376E−02 A₁₂ = −8.934E−03,A₁₄ = 1.232E−02, A₁₆ = −1.890E−03 Eighth Surface k = 0.000,  A₄ =−1.534E−02,  A₆ = 3.450E−02,  A₈ = −4.167E−02, A₁₀ = 1.454E−02, A₁₂ =−3.636E−03, A₁₄ = 1.329E−03, A₁₆ = −2.025E−04 Ninth Surface k =−1.541E+01  A₄ = −3.113E−01,  A₆ = 1.666E−01,  A₈ = −4.358E−02, A₁₀ =1.880E−03 A₁₂ = 8.446E−04, A₁₄ = 1.385E−04, A₁₆ = −4.609E−05 TenthSurface k = −1.353E+01  A₄ = −1.766E−01,  A₆ = 8.321E−02,  A₈ =−3.230E−02, A₁₀ = 9.143E−03, A₁₂ = −1.783E−03, A₁₄ = 2.034E−04, A₁₆ =−1.120E−05

The values of the respective conditional expressions are as follows:

f2/f=−0.513f1/f2=−0.920R2f/R2r=5.949f3/f=5.359Z_(0.7)/f=0.021f34/f=6.041dA/dB=0.1619

Accordingly, the imaging lens of this Numerical Data Example 3 satisfiesthe respective conditional expressions (1) to (15).

FIG. 8 shows the lateral aberration that corresponds to the image heightratio H in the imaging lens of Numerical Data Example 3. Furthermore,FIG. 9 shows a spherical aberration (mm), an astigmatism (mm), and adistortion (%), respectively. As shown in FIGS. 8 and 9, also with theimaging lens of this Numerical Data Example 3, the image surface issatisfactorily corrected and aberrations are suitably corrected,similarly to Numerical Data Example 1.

NUMERICAL DATA EXAMPLE 4

Basic lens data are shown below.

f = 6.207 mm, Fno = 3.79, ω = 24.28° Unit: mm Surface Data SurfaceNumber i R d Nd νd (Object) ∞ ∞  1* (Stop) 1.594 0.899 1.5346 56.0(=νd1)  2* −6.338 0.049  3* 7.593 (=R2f) 0.407 1.6142 26.0 (=νd2)  4*1.281 (=R2r) 0.475 (=dA)  5* 4.458 0.592 1.5346 56.0 (=νd3)  6* 5.4940.618 (=dB)  7* −3.959 0.482 1.6142 26.0 (=νd4)  8* −4.223 0.192  9*3.908 0.852 1.5346 56.0 (=νd5) 10* 2.645 0.235 11 ∞ 0.300 1.5163 64.1212 ∞ 1.001 (Image Plane) ∞ f1 = 2.481 mm f2 = −2.573 mm f3 = 36.884 mmf4 = −335.148 mm f5 = −20.010 mm f34 = 43.214 mm Z_(0.7) = 0.176 mm L =6.00 mm Aspheric Surface Data First Surface k = 0.000,  A₄ = 1.075E−04, A₆ = 6.187E−03,  A₈ = 1.284E−02, A₁₀ = −4.704E−03 Second Surface k =0.000,  A₄ = 1.530E−01,  A₆ = 1.715E−01,  A₈ = −4.549E−01, A₁₀ =2.515E−01 Third Surface k = 0.000,  A₄ = 4.820E−02,  A₆ = 2.777E−01,  A₈= −5.954E−01, A₁₀ = 2.648E−01 Fourth Surface k = 0.000,  A₄ =−1.467E−01,  A₆ = 4.135E−01,  A₈ = −5.821E−01, A₁₀ = 2.475E−01 FifthSurface k = 0.000,  A₄ = −8.933E−02,  A₆ = 1.622E−01,  A₈ = −6.379E−02,A₁₀ = 2.913E−03 Sixth Surface k = 0.000,  A₄ = −7.999E−02,  A₆ =1.406E−01,  A₈ = −2.176E−01, A₁₀ = 2.425E−01, A₁₂ = −1.261E−01, A₁₄ =2.610E−02, A₁₆ = −1.113E−03 Seventh Surface k = 0.000,  A₄ = 1.641E−01, A₆ = −2.353E−01,  A₈ = 1.446E−01, A₁₀ = −5.362E−02 A₁₂ = −7.907E−03,A₁₄ = 1.249E−02, A₁₆ = −2.055E−03 Eighth Surface k = 0.000,  A₄ =−2.186E−02,  A₆ = 3.785E−02,  A₈ = −4.121E−02, A₁₀ = 1.436E−02, A₁₂ =−3.702E−03, A₁₄ = 1.329E−03, A₁₆ = −1.831E−04 Ninth Surface k =−1.497E+02,  A₄ = −3.066E−01,  A₆ = 1.696E−01,  A₈ = −4.330E−02, A₁₀ =2.012E−03, A₁₂ = 8.540E−04, A₁₄ = 1.332E−04, A₁₆ = −5.106E−05 TenthSurface k = −5.878E+01,  A₄ = −1.709E−01,  A₆ = 7.618E−02,  A₈ =−2.994E−02, A₁₀ = 9.138E−03, A₁₂ = −1.841E−03, A₁₄ = 1.982E−04, A₁₆ =−9.281E−06

The values of the respective conditional expressions are as follows:

f2/f=−0.415f1/f2=−0.964R2f/R2r=5.927f3/f=5.942Z_(0.7)/f=0.028f34/f=6.962dA/dB=0.769

Accordingly, the imaging lens of this Numerical Data Example 4 satisfiesthe respective conditional expressions (1) to (15).

FIG. 11 shows the lateral aberration that corresponds to the imageheight ratio H in the imaging lens of Numerical Data Example 4.Furthermore, FIG. 12 shows a spherical aberration (mm), an astigmatism(mm), and a distortion (%), respectively. As shown in FIGS. 11 and 12,also with the imaging lens of this Numerical Data Example 4, the imagesurface is satisfactorily corrected and aberrations are suitablycorrected, similarly to Numerical Data Example 1.

NUMERICAL DATA EXAMPLE 5

Basic lens data are shown below.

f =4.335 mm, Fno = 2.40, ω = 31.92° Unit: mm Surface Data Surface Numberi R d Nd νd (Object) ∞ ∞  1* (Stop) 1.473 0.676 1.5346 56.0 (=νd1)  2*−13.513 0.022  3* 7.452 (=R2f) 0.315 1.6142 26.0 (=νd2)  4* 1.721 (=R2r)0.424 (=dA)  5* 3.881 0.342 1.5346 56.0 (=νd3)  6* 5.288 0.512 (=dB)  7*−6.039 0.379 1.6142 26.0 (=νd4)  8* −6.720 0.083  9* 2.418 0.727 1.534656.0 (=νd5) 10* 1.735 0.320 11 ∞ 0.300 1.5163 64.12 12 ∞ 0.616 (ImagePlane) ∞ f1 = 2.524 mm f2 = −3.722 mm f3 = 26.171 mm f4 = −123.252 mm f5= −18.250 mm f34 = 33.700 mm Z_(0.7) = 0.107 mm L = 4.61 mm AsphericSurface Data First Surface k = −2.291E−02,  A₄ = −7.294E−03,  A₆ =−1.200E−02,  A₈ = 2.498E−02, A₁₀ = −3.959E−02 Second Surface k = 0.000, A₄ = −1.044E−02,  A₆ = 1.227E−01,  A₈ = −1.891E−01, A₁₀ = 4.959E−02Third Surface k = 1.250E+01,  A₄ = −9.164E−02,  A₆ = 3.173E−01,  A₈ =−3.816E−01, A₁₀ = 1.484E−01 Fourth Surface k = 0.000,  A₄ = −7.290E−02, A₆ = 2.383E−01,  A₈ = −1.853E−01, A₁₀ = 9.753E−02 Fifth Surface k =3.341E−01,  A₄ = −9.001E−02,  A₆ = 6.729E−02,  A₈ = −2.705E−02, A₁₀ =1.231E−02 Sixth Surface k = 5.595E−01,  A₄ = −8.905E−02,  A₆ =9.283E−02,  A₈ = −1.770E−01, A₁₀ = 2.265E−01, A₁₂ = −1.565E−01, A₁₄ =5.876E−02, A₁₆ = −9.116E−03 Seventh Surface k = −3.812,  A₄ = 1.386E−01, A₆ = −1.734E−01,  A₈ = 6.787E−02, A₁₀ = −2.732E−02 A₁₂ = −1.570E−03Eighth Surface k = 7.754,  A₄ = −2.881E−03,  A₆ = 1.415E−02,  A₈ =−3.074E−02, A₁₀ = 9.835E−03, A₁₂ = −2.390E−03, A₁₄ = 3.110E−04, A₁₆ =7.347E−05 Ninth Surface k = −1.086,  A₄ = −3.483E−01,  A₆ = 1.374E−01, A₈ = −2.554E−02, A₁₀ = 8.144E−04, A₁₂ = 4.823E−04, A₁₄ = −4.995E−05,A₁₆ = −4.697E−06 Tenth Surface k = −4.595,  A₄ = −1.572E−01,  A₆ =6.504E−02,  A₈ = −2.245E−02, A₁₀ = 4.885E−03, A₁₂ = −6.066E−04, A₁₄ =3.591E−05, A₁₆ = −1.270E−06

The values of the respective conditional expressions are as follows:

f2/f=−0.859f1/f2=−0.678R2f/R2r=4.330f3/f=6.037Z_(0.7)/f=0.025f34/f=7.774dA/dB=0.828

Accordingly, the imaging lens of this Numerical Data Example 5 satisfiesthe respective conditional expressions (1) to (15).

FIG. 14 shows the lateral aberration that corresponds to the imageheight ratio H in the imaging lens of Numerical Data Example 5.Furthermore, FIG. 15 shows a spherical aberration (mm), an astigmatism(mm), and a distortion (%), respectively. As shown in FIGS. 14 and 15,also with the imaging lens of this Numerical Data Example 5, the imagesurface is satisfactorily corrected and aberrations are suitablycorrected, similarly to Numerical Data Example 1.

NUMERICAL DATA EXAMPLE 6

Basic lens data are shown below.

f =3.979 mm, Fno = 2.31, ω = 33.16° Unit: mm Surface Data Surface Numberi R d Nd νd (Object) ∞ ∞  1* (Stop) 1.590 0.600 1.5346 56.0 (=νd1)  2*−16.560 0.060  3* 8.436 (=R2f) 0.320 1.6142 26.0 (=νd2)  4* 1.883 (=R2r)0.335 (=dA)  5* 10.292 0.473 1.5346 56.0 (=νd3)  6* −167.773 0.415 (=dB) 7* −15.454 0.400 1.6142 26.0 (=νd4)  8* −17.008 0.141  9* 1.471 0.6821.5346 56.0 (=νd5) 10* 1.217 0.235 11 ∞ 0.300 1.5163 64.12 12 ∞ 0.753(Image Plane) ∞ f1 = 2.745 mm f2 = −4.022 mm f3 = 18.155 mm f4 =−305.302 mm f5 = −205.163 mm f34 = 19.440 mm Z_(0.7) = 0.066 mm L = 4.61mm Aspheric Data First Surface k = 0.000,  A₄ = −8.004E−04,  A₆ =−8.196E−06,  A₈ = 2.416E−02, A₁₀ = −2.586E−02 Second Surface k = 0.000, A₄ = −3.486E−02,  A₆ = 2.044E−01,  A₈ = −2.800E−01, A₁₀ = 9.556E−02Third Surface k = 0.000,  A₄ = −1.388E−01,  A₆ = 3.993E−01,  A₈ =−5.544E−01, A₁₀ = 2.433E−01 Fourth Surface k = 0.000,  A₄ = −1.172E−01, A₆ = 3.061E−01,  A₈ = −3.445E−01, A₁₀ = 1.675E−01 Fifth Surface k =0.000,  A₄ = −1.459E−01,  A₆ = 1.994E−01,  A₈ = −1.359E−01, A₁₀ =5.642E−02 Sixth Surface k = 0.000,  A₄ = −1.874E−01,  A₆ = 2.176E−01, A₈ = −2.585E−01, A₁₀ = 1.688E−01, A₁₂ = −1.241E−02, A₁₄ = −3.692E−02,A₁₆ = 1.556E−02 Seventh Surface k = 0.000,  A₄ = 1.025E−01,  A₆ =−1.608E−01,  A₈ = 8.611E−02, A₁₀ = −2.751E−02 A₁₂ = −4.373E−03, A₁₄ =1.437E−03, A₁₆ = 2.803E−05 Eighth Surface k = 0.000,  A₄ = −6.126E−02, A₆ = 1.017E−01,  A₈ = −7.748E−02, A₁₀ = 2.308E−02, A₁₂ = −3.258E−03,A₁₄ = 1.012E−04, A₁₆ = 5.961E−05 Ninth Surface k = −3.380,  A₄ =−3.407E−01,  A₆ = 1.849E−01,  A₈ = −4.941E−02, A₁₀ = −1.273E−04, A₁₂ =1.372E−03, A₁₄ = 3.205E−04, A₁₆ = −8.787E−05 Tenth Surface k = −3.760, A₄ = −1.538E−01,  A₆ = 6.762E−02,  A₈ = −2.105E−02, A₁₀ = 3.332E−03,A₁₂ = −2.907E−04, A₁₄ = 2.443E−05, A₁₆ = −2.729E−06

The values of the respective conditional expressions are as follows:

f2/f=−1.011f1/f2=−0.682R2f/R2r=4.480f3/f=4.563Z_(0.7/f=)0.01f34/f=4.886dA/dB=0.807

Accordingly, the imaging lens of this Numerical Data Example 6 satisfiesthe respective conditional expressions (1) to (15).

FIG. 17 shows the lateral aberration that corresponds to the imageheight ratio H in the imaging lens of Numerical Data Example 6.Furthermore, FIG. 18 shows a spherical aberration (mm), an astigmatism(mm), and a distortion (%), respectively. As shown in FIGS. 17 and 18,also with the imaging lens ofthis Numerical Data Example 6, the imagesurface is satisfactorily corrected and aberrations are suitablycorrected, similarly to Numerical Data Example 1.

Accordingly, when the imaging lens of the respective embodiments areapplied to an imaging optical system of a cellular phone, a digitalstill camera, a portable information terminal, a security camera, avehicle onboard camera, a network camera, and the like, it is possibleto attain both high performances and miniaturization of such cameras.

Here, the imaging lens of the invention is not limited to theabove-described embodiments. While all surfaces of the first lens L1 tothe fifth lens L5 are formed as aspheric surfaces in the above-describedembodiments, it is not necessary to form all the surfaces as asphericsurfaces. It is possible to form one or both of the lens surfaces of thefirst lens L1 to the fifth lens L5 as spherical surfaces.

The invention is applicable to an imaging lens for mounting in a devicethat requires a small size and satisfactory aberration correctionability as an imaging lens, for example, a cellular phone or a digitalstill camera.

The disclosure of Japanese Patent Application No. 2011-143711, filed onJun. 29, 2011 is incorporated in the application by reference.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

What is claimed is:
 1. An imaging lens comprising: a first lens havingpositive refractive power; a second lens having negative refractivepower; a third lens having positive refractive power; a fourth lenshaving negative refractive power; and a fifth lens having object-sideand image plane-side surfaces thereof being aspheric, arranged in thisorder from an object side to an image plane side, wherein said firstlens has a shape so that a curvature radius of a surface thereof on theobject side is positive, said fifth lens has a shape so that a curvatureradius of the surface thereof on the object side and a curvature radiusof the surface thereof on the image plane side are positive, and saidsecond lens, said third lens, and said fourth lens are arranged so thatthe following conditional expression is satisfied:0.3<dA/dB<2.0 where dA is a distance on an optical axis from a surfaceof the second lens on the image plane side to a surface of the thirdlens on the object side, and dB is a distance on the optical axis from asurface of the third lens on the image plane side to a surface of thefourth lens on the object side.
 2. The imaging lens according to claim1, wherein said fifth lens has negative refractive power.
 3. The imaginglens according to claim 1, wherein said first lens has a focal lengthf1, said second lens has a focal length f2, said third lens has a focallength f3, said fourth lens has a focal length f4, and said fifth lenshas a focal length f5 so that the following conditional expressions aresatisfied:f1<f3|f2|<f3f3<|f4||f2|<|f5|.
 4. The imaging lens according to claim 1, wherein said secondlens has a shape so that a curvature radius of a surface thereof on theobject side and a curvature radius of the surface thereof on the imageplane side are positive, and said third lens has a shape so that acurvature radius of the surface thereof on the object side is positive.5. The imaging lens according to claim 1, wherein said first lens has anAbbe's, number νd1, said second lens has an Abbe's number νd2, saidthird lens has an Abbe's number νd3, said fourth lens has an Abbe'snumber νd4, and said fifth lens has an Abbe's number νd5 so that thefollowing conditional expressions are satisfied:4.5<νd1<85μd2<3545<νd3<85νd4<354.5<νd5<85.
 6. The imaging lens according to claim 1, wherein saidsecond lens has a focal length f2 so that the following conditionalexpression is satisfied:−1.5<f2/f<−0.4 where f is a focal length of a whole lens system.
 7. Theimaging lens according to claim 1, wherein said first lens has a focallength f1 and said second lens has a focal length f2 so that thefollowing conditional expression is satisfied:−1.0<f1/f2<−0.5.
 8. The imaging lens according to claim 1, wherein saidsecond lens has a shape so that a surface thereof on the object side hasa curvature radius R2f and a surface thereof on the image plane side hasa curvature radius R2r so that the following conditional expression issatisfied:3.0<R2f/R2r<6.0.
 9. The imaging lens according to claim 1, wherein saidthird lens has a focal length f3 so that the following conditionalexpression is satisfied:3.0<f3/f<7.0 where f is a focal length of a whole lens system.
 10. Theimaging lens according to claim 1, wherein said third lens has a shapeso that a surface thereof on the object side has a maximum effectivediameter φ_(3A) and a surface thereof on the image plane side has amaximum effective diameter φ_(3B), and said fourth lens has a shape sothat a surface thereof on the object side has a maximum effectivediameter φ_(4A) and a surface thereof on the image plane side has amaximum effective diameter φ_(4B) so that the following conditionalexpression is satisfied:Z _(0.7) /f<0.1 where Z_(0.7) is an absolute value of a maximum sag upto 70% of the maximum effective diameters φ_(3A) to φ_(4B), and f is afocal length of a whole lens system.
 11. The imaging lens according toclaim 1, wherein said third lens and said fourth lens have a compositefocal length f34 so that the following conditional expression issatisfied:2.0<f34/f<10.0 where f is a focal length of a whole lens system.
 12. Animaging lens comprising: a first lens having positive refractive power;a second lens having negative refractive power; a third lens havingaspheric surfaces; a fourth lens having negative refractive power; and afifth lens having aspheric surfaces, arranged in this order from anobject side to an image plane side, wherein said first lens has a shapeso that a curvature radius of a surface thereof on the object side ispositive, said second lens has a shape so that a curvature radius of asurface thereof on the object side and a curvature radius of a surfacethereof on the image plane side are positive, said third lens has ashape so that a curvature radius of a surface thereof on the object sideis positive, said fourth lens has a shape so that a curvature radius ofa surface thereof on the object side and a curvature radius of a surfacethereof on the image plane side are negative.
 13. The imaging lensaccording to claim 12, wherein said third lens has positive refractivepower, and said fifth lens has negative refractive power.
 14. Theimaging lens according to claim 12, wherein said fifth lens has a shapeso that a curvature radius of a surface thereof on the object side and acurvature radius of a surface thereof on the image plane side arepositive.
 15. The imaging lens according to claim 12, wherein said firstlens has a focal length f1, said second lens has a focal length f2, saidthird lens has a focal length f3, said fourth lens has a focal lengthf4, and said fifth lens has a focal length f5 so that the followingconditional expressions are satisfied:f1<f3|f2|<f3f3<|f4||f2|<|f5|.
 16. The imaging lens according to claim 12, wherein saidfirst lens has an Abbe's number νd1, said second lens has an Abbe'snumber νd2, said third lens has an Abbe's number νd3, said fourth lenshas an Abbe's number νd4, and said fifth lens has an Abbe's number νd5so that the following conditional expressions are satisfied:45<νd1<85νd2<3545<νd3<85νd4<3545<νd5<85.
 17. The imaging lens according to claim 12, wherein saidsecond lens has a focal length f2 so that the following conditionalexpression is satisfied:−1.5<f2/f<−0.4. where f is a focal length of a whole lens system. 18.The imaging lens according to claim 12, wherein said first lens has afocal length f1 and said second lens has a focal length f2 so that thefollowing conditional expression is satisfied:−1.0<f1/f2<−0.5.
 19. The imaging lens according to claim 12, whereinsaid second lens has the shape so that the surface thereof on the objectside has the curvature radius R2f and the surface thereof on the imageplane side has the curvature radius R2r so that the followingconditional expression is satisfied:3.0<R2f/R2r<6.0.
 20. The imaging lens according to claim 12, whereinsaid third lens has a focal length f3 so that the following conditionalexpression is satisfied:3.0<f3/f<7.0 where f is a focal length of a whole lens system.
 21. Theimaging lens according to claim 12, wherein said third lens has theshape so that the surface thereof on the object side has a maximumeffective diameter φ_(3A) and a surface thereof on the image plane sidehas a maximum effective diameter φ_(3B), and said fourth lens has theshape so that the surface thereof on the object side has a maximumeffective diameter φ_(4A) and the surface thereof on the image planeside has a maximum effective diameter φ_(4B) so that the followingconditional expression is satisfied:Z _(0.7) /f<0.1 where Z_(0.7) is an absolute value of a maximum sag upto 70% of the maximum effective diameters φ_(3A) to φ_(4B), and f is afocal length of a whole lens system.
 22. The imaging lens according toclaim 12, wherein said third lens and said fourth lens have a compositefocal length f34 so that the following conditional expression issatisfied:2.0<f34/f<10.0. where f is a focal length of a whole lens system. 23.The imaging lens according to claim 12, wherein said second lens, saidthird lens, and said fourth lens are arranged so that the followingconditional expression is satisfied:0.3<dA/dB<2.0 where dA is a distance on an optical axis from the surfaceof the second lens on the image plane side to the surface of the thirdlens on the object side, and dB is a distance on the optical axis from asurface of the third lens on the image plane side to the surface of thefourth lens on the object side.